Optical pressure detectors with a light-guide affixed to a contact pad are used illustratively as optical alarms sensing a change in the compression applied to the contact pad for instance by someone stepping on it or by removing an object previously resting on it and then triggering a corresponding alarm signal; they are also used in pressure sensors such as weighing scales with which the weight of an object on the contact pad can be measured.
Such pressure detectors operate on a physical principle described illustratively by T. G. Giallenzori et al in "Optical Fiber Sensor Technology", IEEE Journal of Quantum Electronics, QE 18, #4, April 1982. Thereby a compression of the contact pad or the decrease in compression of such a pad entails a change in the light-guide curvature in turn entailing a change in light transmission from the light source to the light detector. The change in light passing through the light guide sensed by the detector is analyzed and, depending on the application, is transduced into an alarm or measurement signal.
Such light-guide curving may be achieved in a number of ways. One way, is to configure the contact pad inside and at least on one side of the light guide in spatially periodic manner, whereby the compression applied to the contact pad is transmitted at periodically spaced sites to the light guide which thereby is then periodically curved.
Another way to achieve periodic curving of the light guide and illustratively described in the European patent document 0,131,474 B1, is to coil a metallic helix around the light guide, said helix being would at a constant pitch around it. In this embodiment, the compression applied to the contact pad is transmitted through the helix to the light guide which thereby is curved periodically.
A common feature of the known pressure detectors is that the losses of transmitted light produced by the curvature of the light guide, which as a rule will be a fiber optics, are detected and analyzed. The particular sensitivity depends on the extent of the deformation of the light guide and on the ensuing light loss of the light moving through the light guide.
The object of the invention is to so design an optical pressure detector evincing a higher sensitivity.